Enantioselective Synthesis of Allylic Boronates bearing a Stereodefined (E)-Alkenyl Chloride by Cu-Catalyzed Borylation of Allylic gem-Dichlorides

Abstract

Chiral α,γ-substituted allyl boron reagents are valuable tools in organic synthesis. However, asymmetric catalytic strategies for synthesising this type of compounds bearing a stereodefined alkenyl chloride are underdeveloped. Here we report a copper-catalyzed enantioselective borylation of allylic gem-dichlorides that provides optically active allylic boronates bearing an (E)-configured alkenyl chloride with high levels of enantioselectivity and E-selectivity. These enantioenriched allyl boronates serve as versatile building blocks for different stereospecific reactions, including their conversion into chiral propargyl alcohols and the diastereoselective addition to ketones to afford enantioenriched allylic chlorohydrins. DFT calculations provide mechanistic insight, revealing key noncovalent interactions that rationalize the observed stereocontrol. This study expands the synthetic utility of allylic boronates and offers a mechanistically informed approach to asymmetric catalysis involving gem-dichloride substrates.